This invention relates to security chain locks for doors, and particularly to an improved chain lock which resists forced entry better than presently known chain locks.
Security chain locks for doors have long been known. Their function is to permit a door to be cracked open from within, without permitting a person outside the door to enter. Generally, they allow the door to open sufficiently to see the outside, but less than six inches. Such locks include a first keeper element attached to the door, near the free vertical edge of the door, a second keeper element on the door frame, and a flexible element connected between the first and second keeper elements. The second keeper element is mounted adjacent the first keeper element on the door frame. It will be understood that the "frame" may be the side jamb, casing or trim, depending on the construction of the door and the length of the screws holding the second keeper element. The flexible element is traditionally a chain, although other flexible elements such as cables are also sometimes used. Any such flexible element will be referred to hereinafter as a chain.
A traditional chain lock is vulnerable to forced entry. The traditional chain lock is effective against casual intruders, but when a person of substantial size throws his or her weight against the door or kicks the door, one of the keeper elements frequently pulls out of the door frame or door. Therefore, the chain lock frequently gives a false sense of security and in some ways is worse than nothing. The problem may be reduced by using longer, heavier screws to attach the keeper elements, but there are practical limitations to this solution.